Use MM decomp names for some unnamed code files

[cadmic]

I'm going on a crusade to name all the code_80XXXXXX.c files because I have a lot of trouble telling them apart. The files in this PR are named in MM decomp already, so while the names aren't be perfect I think it's a good starting point.

code_800430A0.c => z_bg_collect.c
code_80043480.c => z_bg_item.c
code_8006C3A0.c => z_env_flags.c
code_80097A00.c => z_inventory.c
code_800FC620.c => system_heap.c

[Pepe20129]

Looks good, although it seems that z_inventory was probably originally called z_save and z_env_flags was probably something like z_f_env due to the ordering.

[cadmic]

yeah I agree, and personally I would like to names these closer to what we think the original names are, but it seems like the precedent is to not care about that (e.g. z_rumble vs z_vibrate)

[fig02]

One day when the "original filename" section exists on every file, we can add our speculations of what original filenames might have been.